1. Field of the Invention
The invention relates to a device for rearranging poison rod assemblies positioned in a fuel assembly between a plurality of fuel assemblies and, more particularly, relates to a motorized device for such rearranging of the poison rod assemblies between fuel assemblies.
2. Description of the Prior Art
In a commercial nuclear reactor, heat, from which steam and ultimately electricity are generated, is produced by fissioning of a fissible material, such as enriched uranium, contained in a reactor vessel. The reactor vessel includes a flanged closure head bolted atop a flanged reactor body; the reactor vessel being entirely contained within a containment building. This fissile material, or nuclear fuel, is typically contained within a reactor nuclear core formed from a multiplicity of fuel rods supported in a plurality of nuclear fuel assemblies, coextensively arranged in a spaced parallel array.
In addition, poison rods are dispersed throughout the core and, more specifically, throughout the fissionable material to properly disperse the fissionable process within the core. The poison rods generally include a plurality of elongated rods each containing neutron absorbing materials which fit in longitudinal openings defined in the fuel assemblies. A web shaped top portion joins the poison rods together forming a poison rod assembly. A T-shaped bar is affixed atop the web shaped top forming an easily accessible handle for lifting the poison rod assemblies during maintenance or the like.
During such maintenance, refueling or the like, the reactor closure head is unbolted, and the fuel assemblies, containing the poison rod assemblies, are removed from the reactor vessel, transported to a fuel storage building and positioned in storage racks by means well known in the art. The fuel storage building may contain water having boric acid therein for properly storing the fuel assemblies. The storage racks include a plurality of cavities coextensively arranged in a spaced apart, rectangular array, although any shaped array may be utilized. The poison rod assemblies are then repositioned between different fuel assemblies so that unusable poison rod assemblies are mated with unusable fuel rods forming a spent fuel assembly. After a sufficient decay period, the spent fuel assemblies are removed from the storage racks and loaded into a shipping cask for removal from the site.
A presently known and utilized device for rear-ranging the poison rod assemblies between the fuel assemblies includes a platform which is suspended over the fuel assemblies by a movable bridge. A manually operated winch is positioned on the platform and includes a cable attached to an elongated, tubular member having two notches for lifting the poison rod assemblies. An actuator is also positioned on the platform and communicates with the tubular member for circularly rotating the tubular member into a position which latches the notches onto the T-shaped bar of the poison rod assembly.
To remove a poison rod assembly, the winch is manually cranked which, in turn, lowers the tubular member to a position adjacent the T-shaped bar of the poison rod assembly. The actuator communicates with and circularly rotates the tubular member thereby passing the notches of the tubular member around the T-shaped bar. After the actuator moves the tubular member into the latched position, the winch is again cranked by maintenance personnel standing on the movable bridge, and this cranking, thus, lifts the poison rod assembly from the fuel assembly. The movable bridge is maneuvered over another fuel assembly, and the poison rod assembly is lowered into a predetermined fuel assembly by the winch. The actuator then rotates the tubular member to detach the tubular member from the T-shaped bar of the poison rod assembly. The above described process is then repeated for repositioning other poison rod assemblies.
Although the present device for rearranging the poison rod assemblies is satisfactory, it is not without drawbacks. When a large quantity of poison rod assemblies are required to be rearranged, as is usually the case, the present method is time consuming partially because of the time it takes to manually manipulate the winch.
Consequently, a need exists for an improved device for rearranging poison rod assemblies between a plurality of fuel assemblies.